GaN-based LED (light-emitting Diode) is a kind of novel luminescent device known as solid state light source in 21 century, which possesses many advantages such as compactness, low energy-consumption, long Life of permanence, free of mercury, high efficiency, and low ratio of service. It can be used widely in a variety of lighting fixtures including interior illumination, traffic signal/indicator lamp, automobile tail light/head light, large scale screen used outdoors, display screen and advertisement screen, and trends to replace bulb and fluorescent lamp that used currently. The novel environment-friendly light source will dominate the development of the lighting system and play an important role in energy-saving, environmental protection, and improvement of the life quality. The fabrication technique comprises mainly (1) combination of three kinds of monochromatic LED (blue, green, red); (2) combination of blue light LED with yellow fluorescent powder; (3) combination of ultraviolet LED with trichromatic red-green-blue fluorescent powder. However, inorganic luminescent material that can be excited effectively by blue-light LED is seldom. Presently, white light is mainly obtained based on complementary color theory through the combination of YAG:Ce fluorescent material of Yttrium-Aluminium-Garnet structure with blue light LED. Since the light emitted from YAG is yellow-green, however, the obtained white light is characterized to have high color temperature and cool tone so that the coloration indexing is not satisfactory. As a result, green, yellow or red fluorescent powder is added to acquire white light with different color temperature (from cool tone to warm tone) and improve the coloration indexing.
Presently, most of the red fluorescent material that can be excited by blue light (420-480 nm) is sulfide doped with bivalent europium, for example, (Ca,Sr,Ba)S:Eu2+. And most of the green fluorescent material that can be excited by blue light (420-480 nm) is sulfide doped with bivalent europium, for example, (Ca,Sr,Ba)GaS4:Eu2+. But, sulfide fluorescent powder is active and unstable thermally, it tends to react with the water in air and decompose while heated. In addition, the environment will be polluted by waste gas exhaust during the production of sulfide. Employment of nitride, formed of SiN4 units, as the matrix of fluorescent powder attaches considerable attention recently. While doped with rare-earth element such as europium, due to the strong covalent link and big crystal field splitting, this type of compound can emit light with large wavelength such as yellow, orange and red light. European patent (PCT/EP2000/012047) described a red fluorescent powder M2Si5N8:Eu2+ (M=Ca, Sr, Ba) and the preparation method thereof. The fluorescent powder is stable chemically and thermally, and can be excited by blue light. Otherwise, luminescent intensity of said fluorescent powder needs to be improved.